For users staying in indoor environment, in-building mobile communications services should be available to effectively cover and connect different indoor public places. Among the available in-building mobile communications services, one of the fastest growing services is an Indoor Positioning Solution (IPS). The IPS is primarily driven by two major requirements—emergency services and commercial applications. The emergency services should be able to provide locations of emergency callers with considerable degrees of accuracy and reliability. The commercial applications should be able to perform a fast and accurate positioning for a wide variety of commercial services, such as indoor maps, location based advertising and social network services.
In outdoor environment, sufficient location signals such as Global Navigation Satellite System (GNSS) signals are provided to determine a position of a mobile device. On the other hand, the indoor environment is subjected to higher interference and penetration loss of Radio Frequency (RF) signals than the outdoor environment. In some cases, even the best assisted GNSS signal does not reach some areas in the indoor environment.
As indoor positioning methods without using the GNSS signals, methods using Bluetooth or Wi-Fi technology may be used. However, in the method using Bluetooth or Wi-Fi technology, additional equipment should to be installed at both the network-side and the handset-side in order to determine positions of legacy mobile devices which do not support Bluetooth or Wi-Fi technology.
Alternatively, an actual indoor mobile communication system may be implemented using an indoor repeater system, where a macro-cell's coverage is divided into a plurality of repeated cells. Here, a remote unit is assigned to each of the repeated cells to provide the in-building mobile communications services in the repeated cells. The indoor repeater can increase the cell capacity of the mobile cellular system in the indoor environment. However, the indoor repeater system may not be suitable for the emergency services and the commercial applications for the following reasons.
First, signals in the indoor repeater system are subjected to a high signal loss, as described above. Accordingly, it is hard for user equipment in the indoor repeater system to acquire GNSS signals or RF signals strong enough to perform a position determination from satellites or neighboring base stations.
Second, multiple remote units in one macro cell simulcast signals from the same base station. As a result, the user equipment is provided with mobile communications services in a single strong macro cell which is connected via the remote units. In this environment, it is hard to use conventional positioning methods such as triangulation or trilateration using signals from multiple base stations.
Third, all remote units provided in one macro cell have the same cell Identification Number (ID). Accordingly, the user equipment or a location server cannot locate from which remote unit a received signal was transmitted.
Fourth, inherent delays in the indoor repeater system result in positioning estimation errors. In comparison with a system where the user equipment is directly connected to the base station, the indoor repeater system has inherent signal delays such as optic delays and processing delays of the remote units. These inherent delays result in positioning estimation errors up to a few kilometers.